The present invention relates to heaters that utilize particulate solid materials as fuel. More particularly, the present invention is concerned with a stoker assembly for feeding such particulate material to the burner of the heater.
Heaters with some means of feeding combustible particulate material thereto are well known and often referred to as stoker-type heaters. Typically, such stoker-type heaters have been utilized with pulverized coal or some similar combustible particulate material as a fuel source. Such heaters were later replaced by oil or gas-fired heaters when gas and oil were in plentiful supply. Because of increasing costs of gas and oil fuel, attention again is being directed to wood-burning heaters that burn wood or other types of combustible residue. Presently, particular attention is being given to heaters of the type that use preprocessed pelletized fuel sources produced from wood waste, agricultural residue and the like.
A stoker-type heater basically consists of a reservoir for containing the fuel supply, a feed means for conveying the combustible fuel supply from the supply container to the burner in the combustion chamber of the heater and an air supply for use in combustion of the combustible fuel.
In using preprocessed pelletized feed fuel, there are a number of problems that must be overcome that are not encountered when using conventional type fuel supply such as coal or wood chips. The pelletized fuel is prepared by compacting wood waste, agricultural residue, paper, coal dust, or garbage into discrete particles. Such discrete pelletized particles are generally not processed in a manner that results in a pellet which has high structural integrity. Therefore, care must be taken when the pellets are conveyed to the burner of the combustion chamber, not to subject the pellets to any unnecessary movement other than that required to move the pellets from the fuel supply to the combustion chamber. Of particular concern, are systems that utilize a rotary type conveying means whereby the pelletized fuel may be easily ground or crushed up into a powdery residue by the conveying means. The pellets are particularly suspectible to grinding and crushing when they are being introduced into the combustion zone because the pellets may fall back down into the conveying means.
Another problem not specific to preprocessed pelletized fuel is the danger of "burn back" that occurs when the fire on the burner head penetrates upstream through the fuel supply system to the fuel storage bins. One method of addressing this problem incorporates a dual feed system with a "fire break" separating the systems to prevent the burn back. These designs are often cumbersome and expensive. Additionally, there is always a chance that a burn back of intense magnitude could jump the fire break and ignite the fuel storage bins.
Therefore, it is an object of the present invention to provide a feed supply means whereby small pelletized fuel particles can be efficiently and safely transported from a storage chamber to a combustion chamber without being susceptible to burn back or subjected to undesirable crushing or grinding conditions.